High-rate quantum key distribution over 100 km using ultra-low-noise, 2-GHz sinusoidally gated InGaAs/InP avalanche photodiodes

We have demonstrated quantum key distribution (QKD) over 100 km using single-photon detectors based on InGaAs/InP avalanche photodiodes (APDs). We implemented the differential phase shift QKD (DPS-QKD) protocol with electrically cooled and 2-GHz sinusoidally gated APDs. The single-photon detector has a dark count probability of 2.8 × 10(-8) (55 counts per second) with a detection efficiency of 6 %, which enabled us to achieve 24 kbit/s secure key rate over 100 km of optical fiber. The DPS-QKD system offers better performances in a practical way than those achieved using superconducting single-photon detectors. Moreover, the distance that secure keys against the general individual attacks can be distributed has been extended to 160 km.

800 MHz single-photon detection at 1550-nm using an InGaAs/InP avalanche photodiode operated with a sine wave gating

Single-photon detection at 1550-nm with a high repetition rate was realized using an InGaAs/InP avalanche photodiode operated with a sine wave gating. Removing the AC noise due to the transferred gate signal usingband elimination filters, we have discriminated the avalanche signal which is much smaller than that in the conventional gating, which results in the suppression of the afterpulsing. At the repetition frequency of 800MHz, the overall afterpulsing probability was 6.0% with the detection efficiency of 8.5% and the dark count probability of 9.2X10(-6).